The present invention relates generally to semiconductor device processing techniques, and, more particularly, to a method and structure for eliminating aluminum terminal pad material in far back end of line (FBEOL) semiconductor structures.
In semiconductor manufacturing, a fabricated integrated circuit (IC) device is typically assembled into a package to be utilized on a printed circuit board as part of a larger circuit. In order for the leads of the package to make electrical contact with the bonding pads of the fabricated IC device, a metal bond is formed to make a connection between the bonding pad of the IC device and a lead extending to the package lead frame. In other configurations, such as a controlled collapse chip connection (C4), a solder ball connection is made to a ceramic or polymeric chip carrier.
In the past, aluminum and aluminum alloys have been used as conventional chip wiring materials. More recently, aluminum wiring material has been replaced by copper and copper alloys, since copper wiring provides improved chip performance and superior reliability when compared to aluminum and alloys of aluminum. However, the packaging of IC devices employing copper wiring presents a number of technical issues related to the reaction of copper with material used in the solder-ball process and/or susceptibility of copper to environmental attack and corrosion.
In current C4 practice, terminal via openings are formed in a passivation layer to the underlying terminal pad copper wiring level. A terminal metal (TD) aluminum pad structure is then conventionally formed over the terminal pad copper, followed by a final organic passivation layer deposition, patterning and curing process before ball limiting (BLM) metallurgy C4 lead-tin solder balls are used to connect to the TD pad. The TD metal process represents increased manufacturing steps and costs associated with the semiconductor structure. It is thus desirable to eliminate the aluminum TD pad, given the present conversion of all chip wiring from aluminum to copper. However, simply eliminating the manufacturing steps of the TD aluminum structure itself from the process of record would expose the copper to the organic passivation materials and to atmospheric conditions, leading to adverse reactions.